Composite piston



April 25, 1933. J. R. cox 1,905,157

COMPOSITE PISTON Filed May 20, 1931 2 Sheets-Sheet 1 I TU (fa/77771 0036 April 25, 1933. J R cox 1,905,157

Y COMPOSITE PISTON I Filed May 0, 1931 2 Sheets-Sheet 2 Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE JOHN R. COX, OF CLEVELAND, OHIO, ASSIG-NOR TO THOMPSON PRODUCTS, INCORPO- RATED, OF CLEVELAND, OHIO, A. CORPORATION OF OHIO COMPOSITE PISTON Application filed May 20,

This invention relates to composite pistons particularly adapted for use in internal combustion engines.

It is an object of this invention to provide an improved composite piston having a head of good thermal properties together with a skirt of good bearing and wearing properties in engine cylinders, and of material having expansion characteristics closely approximating those of the engine cylinders. I am aware that it has heretofore been proposed to cast an aluminum head about portions of an iron or steel skirt, but it has heretofore been found that such combinations cause an unequal expansion of the, skirt portion which results in distortion thereof, with consequent high spots tending to score the engine cylinder due to the concentrated heat transfer to the skirt at the points where the head is cast thereabout.

It is a further object of this invention to provide a composite piston of the class described wherein the skirt is so shaped as to maintain a cylindrical form in spite of the increased expansibility of the material of the head, thus, by a suitable choice of the skirt material, providing a constant clearance piston of uniform bearing area even at high operating temperatures.

It is well known that a cast iron or steel piston has advantages over an all aluminum piston and vice versa. The composite piston of this invention incorporates the advan tages of each type without the corresponding disadvantages. Thus my composite piston is lighter and has better thermal properties than a cast iron or steel piston, permitting higher compression ratios without the formation of carbon beneath the piston head, or preignition and detonation troubles. As regards an all aluminum piston my composite piston is more economical to manufacture, can be made as light and with the same or better efiiciency, and runs with a constant and smaller clearance, having a better wearing surface and decreased oil consumption.

Other and further important objects of this invention will be apparent from the dis- 1931. Serial No. 538,695.

closures in the specification and the accompanying drawings.

This invention (in a preferred form) is illustrated in the drawings and hereinafter more fully described.

On the drawings:

Figure l is an elevation of a finished composite piston embodying the features of the invention.

Figure 2 is a vertical cross section on the line IIII of Figure 1.

Figure 3 is an elevation of the piston skirt as formed prior to casting the head and pin bosses thereon.

Figure 4 is a bottom view of Figure 3.

As shown:

The piston of this invention comprises a preformed tubuluar skirt portion 10 about portions of which dependent wrist pin bosses 11 are cast integral with a head 12. The head and dependent bosses are preferably cast of a light weight alloy, consisting principally of aluminum or magnesium, for example, having the desirable property of hi h heat transfer capacity, but accompanied by an undesirably large expansion coefficient. Such alloys also exhibit poor wearing qualities in an iron or steel cylinder, being subject to scoring under adverse lubricating conditions so that the piston design as a whole is preferably such that the head portion acts as a heat conductor, and carries piston ring grooves 13 without makin actual contact with the engine cylinder. he head is held in alignment with the cylinder bore by its attached skirt which is of a material having better wearing qualities and less, expansibility than the head and can therefore be fitted with less clearance in the cylinder to prevent cooking of the piston and thus maintain a square seating of the rings against the cylinder walls.

The detail design of the cast head portion is largely a question of providing suflicent strength in the alloy chosen, plus these requirements of heat transfer from the head to the rings and piston bosses. In the design shown the head and pin bosses are strengthened by a rib 14 extending from one boss to the underneath side of the head thence may across the head and down to the other boss. The material of the head is also spread out into a. box-like strut 15 about the material of the skirt adjacent the pin bosses, this box like strut extending up into good structural supporting engagement with the depending ring holding portion of the head since the entire pressure on the piston head is transmitted through these struts 15 and the rib 14 to the wrist pin bosses 11. I The skirt 10, in the case of small quantity production, is preferably cut from a length of seamless tubing. In the case of quantity production it may be preferable to draw the skirt to shape from sheet metal in a cupping press since it is desirable to provide an inturned flange 16 around the bottom or free edge to stiffen the same. Such a flange can be turned over on the end of lengths of tubing by well known methods, and is a necessary part of the drawing method in the case of sheet material. A third method of forming the skirt is to roll it up from lengths of strip material and to weld the abutting edges. In any case the skirt is preferably madefrom a grade of iron or steel alloy having a coeflicient of expansibility approximating that of the material of the engine cylinders, and of good wearing qualities against the cylinder wall. To this end, it

be hardened or heat treated if desired. The skirt 10 is slotted at 17 through a portion of its circumference below this intended location of the pin bosses and struts, in order to facilitate the indentation of the portions of the skirt intended to be imbedded in the depending portions of the cast head. The indentations are preferably formed as a major flat surface 18 about which the struts and pin bosses are cast, which surface merges at the sides into the cylindrical surfaces of the skirt through a tapered surface 19 wide adjacent the head and narrow at the slot 17 This tapered surface or gore 19 has been found to be an essential feature marking as important improvement over prior developments. One explanation is that it apparentl I corresponds to the temperature radient no to the transfer of heat from 518 head to the strut and thence to the skirt. In pistons made without this tapered surface or gore, it has been found that in use the piston skirt showed signs of distortion which resulted in localized high bearing spots or,

scuffed areas at each corner of the cylindrical areas adjacent the piston head. This trouble arose from the push of the expanding piston head and pin bosses which were found to separate about 15 thousandths under normal operating temperatures thus pushing out the bearing areas adjacent the indented areas and in effect flattening or increasing the radius of the cylindrical skirt sections between the pin bosses. I have found that the tapered areas or gores tend to maintain the original profile of the cylindrical skirt areas thus providing a constant clearance skirt that can be fitted in the cylinder with a minimum initial clearance'when cold.

The flatening of the indentured portions 18 presents a problem in the disposal of the excess circumference represented by the length of the cylindrical are which is reduced to a straight line. This may be absorbed by a slight upsetting or thickening of the flattened portion, or by cutting out a section equivalent to the excess length and then welding the severed edges if desired. A third method is to displace the excess metal outwardly to form an interlock 20 with the cast head.

The indentured areas intended to be embedded in the cast pin bosses and struts are perforated at 21 for the wrist pin bearings,- and may be further perforated as at 22 about the pin hole to increase the bond between the cast head and the skirt. The skirt is preferably free from the head except at the strut locations, but the air gap 23 so formed may be out after casting the head in position if so desired.

It will thus be seen that I have invented an improved composite piston wherein the skirt forms the sole bearing surface aside from the rings and the skirt is so formed as to maintain its original cylindrical form and close running clearance at operating temperatures in spite of the excessive expansion of the cast head portion.

I am aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this inven- 2. A composlte piston comprising a cylindrical skirt portion of preformed metal having indentations therein adjacent the wrist 'pin locations, said indentations merging at the sides thereof into the cylindrical surface by means of tapered and beveled intermediate portions, and a cast head portion having depending struts enveloping the indented portions 0 the skirt and embodying wrist pin bearings therein.

3. As an article of manufacture, a pretion, and I, therefore, do not purpose limiting 5 formed skirt for a piston comprising a cylindrical member formed of relatively thin gage metal, an inturned reinforcing flange at one end thereof, diametrically opposite indentations in the cylindrical surface and merging thereinto by means of beveled surfaces taper- 5. A composite piston comprising a skirt head, the indentations of the skirt mer as flat surfaces into the wall thereof in axis throug skirt.

In testimony whereof I have hereunto subscribed m name at Cleveland, Cuyahoga County,0 io.

. JOHN R. COX.

bearing su aces lanes inclined towards a central the wall bearing surfaces of the flattened at the sides between the bearing surfaces thereof, the flattened portions containing wrist pin bearing apertures and merging into the bearing surfaces of the skirt on a graduated taper, and piston head wrist pin bearing portions havin depending enveloplng the flattened portions of partia ly the skirt.

6. A composite piston comprising a skirt of relatively non-expansible material of substantially uniform gage, flattened at the sides between the bearing surfaces thereof the flattened portions containing wrist pin aring apertures and merging into the bearing surfaces ofthe skirt on a graduated taper, and piston heads having depending wrist pin bearing portions embracing the flattened portions ofv the skirt.

7. A piston having a skirt formed from sheet material, the upper portion of which is flattened on opposite sides between the bearing surfaces thereof, the flattened portions having graduated beveled surfaces connected to the bearing surfaces of the skirt, a head of cast material and depending wrist pin bearings integral with the head, said bearings erfiveloping the flattened portions of the piston s irt.

8. A piston comprising a cast metal head and a skirt formed from material of uniform gage, said skirt being circumferentially slotted on opposite sides and having the material above the slots indented, and merging with the bearin surfaces of the skirt through beveled an tapered surfaces, depending'wrist pin bearing bosses and support therefor at opposite sides of the head and integral with said heads, said wrist pin bearing bosses and supports embracing the in dented portions of the skirt.

9. A composite piston com rising a thick sectioned li ht metal head and a thin section heavy metal skirt, the skirt having indentations between the wall bearing surfaces thereof,the indentations of the skirt being enveloped in bosses depending from the piston 

